How to Lower the PH of Aquarium Water

The term pH refers to how acidic or alkaline water is. This is very important for aquariums because most fish have a specific pH range in which they can thrive. For example, angel fish can live in water with a pH between 5.0 and 7.0, while Tanganyikan cichlids require a pH between 7.0 and 9.2.

Things You'll Need

Peat

Hydrocloric acid

Phosphoric acid

Filter the water through peat before you put it into your aquarium to lower the pH of the water.

Treat the water with hydrochloric acid to lower the pH. The amount that you will have to use depends on the buffering capacity of your water.

Use phosphoric acid products, available at most fish stores and online, to lower the pH. The downside of phosphoric acid is it lowers the buffering capabilities of the water, so your tank will be more susceptible to pH swings.

Bubble carbon dioxide gas through your tank. Some of the carbon dioxide will be absorbed in the water as carbonic acid, which will lower the pH. The drawbacks to carbon dioxide gas is that it is expensive, and when the gas is turned off, the pH will revert to its higher value.

Tips & Warnings

Also dangerous for the fish is rapid swings in pH, so it is better to have a constant pH slightly off the ideal than pH that is fluctuating. For example, if a fish's ideal pH is 6.5, it would be better to have a fixed pH of 6.2 than to have a pH that varies from 6.2 to 6.8.